Confocal microscopy was proposed by Marvin Minski (cf. U.S. Pat. No. 3,013,467, Dec. 19, 1961).
The chromatic confocal technique provides the possibility of effecting focusing without the need for mechanically moving parts, which as a result usually reduces measuring time significantly, as was proposed by G. Molesini in 1983 in connection with a spectrometer (cf. GB 2144537 and DE 3428593 C2). An example of successful application of the chromatic confocal approach is described in a paper by H. J. Tiziani and H.-M. Uhde “Three-dimensional image sensing by chromatic confocal microscopy” in Applied Optics, Vol. 33, No. 1, April 1994, pages 1838 to 1843. In this case the spectral analysis is performed using three color filters. Thus, the achievable depth measurement and depth resolution are limited.
DE 103 21 885 A1 describes a chromatic confocal system including a component having variable refractive power, for example, a diffractive component. In the arrangement shown in FIG. 2 of this patent a row of micro-lenses is provided for illumination in order to obtain the confocal signals via the wavelength and, for analysis, a spectrometer containing a planar camera is disposed downstream, so that line profiles may be obtained from a single planar camera image by means of a line spectrometer.
In the publication “Chromatic confocal detection for high speed micro-topography measurements” by A. K. Ruprecht, K. Körner, T. F. Wiesendanger, H. J. Tiziani, W. Osten in Proceedings of SPIE, Vol. 5302-6, pp. 53 to 60, 2004, FIG. 4 shows a chromatic confocal line sensor for topographic measurement. Here, in order to obtain the confocal signals via the wavelength of the chromatic confocal system, a spectrometer is added to the arrangement such that line profiles of the surface of an object may be obtained from a single image using a single planar camera and a line spectrometer. The use of a spectrometer generally allows for better spectral resolution compared with a system incorporation three color filters or an RGB color camera or even a four channel camera, and therefore provides an advantage.
In the aforementioned citations, there is no mention of features concerning three-dimensional measurement of the shape of an object or the shape of a micro-object, meaning the capture of the entire shape of the object using a chromatic confocal technique and spectral analysis by a camera within the timeframe of creating a single image, i.e. the integration time for a camera frame, with which a higher spectral resolution would be obtainable than when using three or four color channels.
On pages 12 and 13 of the dissertation entitled “3D-Spectrophotometry of extragalactic emission lines” by J. Schmoll, submitted to the University of Potsdam in June 2001, lenticular direct coupling is described, which was first applied in the TIGER spectrograph by Courtes et al. in 1988. Here, the lenticular raster is rotated through an angle φ against the direction of dispersion. Because of the shift of adjacent spectra, this technique has the reputation of being complicated for evaluation and the area of the area sensor is not used economically as there is no high area filling factor.
In the scientific literature, terms such as 3D spectrophotography and imaging spectroscopy, and also integral field spectrophotometry are being used.